fix(material/menu): incorrectly detaching lazy content when menu is transferred to a new trigger (#31690)

The menu has some logic that detaches its lazy content when the animation is finished, however while the animation was running, the panel might've been picked up by another trigger. This ends up opening an empty menu panel to the new trigger.

These changes resolve the issue by checking if another trigger picked up the panel before detaching the lazy content.

Fixes #31687.

Author: crisbeto

src/material/menu/menu-trigger-base.ts

@@ -300,7 +300,14 @@ export abstract class MatMenuTriggerBase implements OnDestroy {
     if (menu instanceof MatMenu && this._ownsMenu(menu)) {
       this._pendingRemoval = menu._animationDone.pipe(take(1)).subscribe(() => {
         overlayRef.detach();
-        menu.lazyContent?.detach();
+
+        // Only detach the lazy content if no other trigger took over the menu, otherwise we may
+        // detach something we no longer own. Note that we don't use `this._ownsMenu` here,
+        // because the current trigger relinquishes ownership as soon as the closing sequence
+        // is kicked off whereas the animation takes some time to play out.
+        if (!PANELS_TO_TRIGGERS.has(menu)) {
+          menu.lazyContent?.detach();
+        }
       });
       menu._setIsOpen(false);
     } else {